Nano-powder of metallic zirconium can not exist because it oxidizes to ZrO2 in any atmosphere including the highest possible technical vacuum. Even micro-zirconium powder does not exist in air because it is pyrophoric. Nano-ZrO2 powder is only produced chemically (for example by spray-drying Zr(NO3)4 solution). It is practically impossible to produce the ZrO2 particles smaller than 50 nm by grinding (ball milling) of micro-ZrO2 powder.